1. Field of the Invention
The present invention relates to an organic light emitting display device, and more particularly to an organic light emitting display device in which a voltage drop (i.e., IR drop) can be minimized while using a metal substrate.
2. Description of the Related Art
An organic light emitting display device is a self-luminescent device in which electrons and positive holes injected into organic materials through an anode and a cathode are recombined to generate excitons, and a predetermined wavelength of light beams are generated by energy generated by excitons.
Since the organic light emitting display device does not require a separate light source such as a backlight unit, it can provide some advantages such as low power consumption, a wide angle of view, and a fast response speed in comparison with a liquid crystal display device. Therefore, the organic light emitting display device has been highlighted as a next generation display.
The light emitting elements of the organic light emitting display device include an anode which is an electrode for injecting holes, an organic layer, and a cathode which is an electrode for injecting electrons. The organic layer includes organic materials capable of emitting red, green, and blue light to implement a full-color display.
In addition, the organic layer may have a multi-layer structure that includes an emitting layer (EML), an electron transport layer (ETL), and a hole transport layer (HTL) in order to increase light emitting efficiency by balancing the electrons and the holes. In some cases, the organic layer may further include a separate electron injection layer (EIL) and a hole injection layer (HIL).
Such an organic light emitting display device can be classified into a passive matrix type or an active matrix type, depending on a driving method.
While the passive matrix type of organic light emitting display device has advantages such as a simplified manufacturing process and a low manufacturing cost, it has large power consumption, and does not provide a wide display area.
On the other hand, while the active matrix type organic light emitting display device has shortcomings such as a complicated manufacturing process and a high manufacturing cost in comparison with the passive type of organic light emitting display device, it has advantages such as lower power consumption, a high definition, a fast response speed, a wide angle of view, and a sufficiently thin thickness due to an RGB (red/green/blue) independent drive type.
In addition, the organic light emitting display device can be classified into a bottom emission type, a top emission type, or a dual emission type, depending on a light emitting direction from the organic layer. While the light is emitted in a direction opposite to the substrate having pixels in the top emission type of organic light emitting display device, the light is emitted toward the substrate having pixels in a bottom emission type of organic light emitting display device. The bottom emission type of organic light emitting display device has a relatively high numerical aperture.
Since the light emitted from the organic layer of the pixel is output in a direction opposite to the substrate in the top emission type of organic light emitting display device, one of the anode and the cathode interposing the organic layer should be transparent if the light is output from it.
Typically, the transparent electrode of the organic light emitting display device is formed of a transparent conductive material such as Indium-Tin-Oxide (ITO). Unfortunately, since the transparent conductive material such as ITO has a high resistance value, a voltage drop is generated by the high resistance of the transparent electrode, and irregular brightness is generated in a display device due to the voltage drop.
For this reason, in one of the anode and cathode provided on the top and bottom of the organic layer, and particularly, in reference to the cathode, a cathode power line for supplying a cathode voltage to the cathode is formed of metal. In this case, the cathode voltage provided from the external terminal is applied to the cathode power line, and is provided to the cathode through a contact hole.
However, a voltage drop is generated from such a cathode wire line itself, and a pixel area is limited by the space occupied by the cathode wire line.